Segment Reporting Segment Asset Reconciliation (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Segment Reporting [Abstract]
Segment Assets	$ 38,148	$ 36,850	$ 39,108
Corporate Assets	4,401	5,799	3,870
Total Assets	$ 42,549	$ 42,649	$ 42,978